This invention relates to electrically conductive portland cement mixtures and particularly to backfill materials for ground bed anodes such as those described in U.S. Pat. No. 3,725,669 to Joe F. Tatum and U.S. Pat. No. 4,786,388 to Joseph F. Tatum, Jr.
The well-known practice of using deep well anode beds to prevent corrosion and rapid deterioration of subsurface metallic structures is referred to in those patents.
In deep well cathodic protection systems the wells may run from fifty feet to several hundred feet deep. Such wells may pass through one or more strata of water. In such case the installation of the well may provide a passage between one or more water layers, and possibly a porous layer. In either situation the possibility of contamination between layers is possible. Such contamination may result in undesirable effects and be contrary to environmental considerations.
Accordingly, in U.S. Pat. No. 4,786,388 a backfill composition is described which includes a portland cement so that a solid, non-porous, backfill is provided which does not permit the transfer of liquids between different levels. In order to provide the backfill composition with the required characteristic of conductivity, the portland cement is mixed with calcined fluid petroleum coke and with naturally occurring graphite flakes or graphite powder. The use of the coke requires a high proportion thereof with the result that the cement composition may not always set as much like conventional cement as desired. Furthermore, the ability of the graphite to conduct current is of a limited nature. In addition, a surfactant is required to facilitate pumping of the material.
It will be apparent, therefore, that the use of conductive substances tends to detract from the quality o the cement product. Hence the selection of conductive materials which will provide a high level of conductivity at low levels of proportion is desired in order that high cement quality may be maintained.